Stropping device



Original Filed Feb. 25, 1929 H1." Ill lll HI llll 1 Hr L Patented May 25, 1937 UNITED STES Asst orsies Application February 25, 1929, Serial No. 342,387 Renewed August 18, 1936 7 Claims.

My invention relates to mechanical stropping means intended to produce a very fine, sharp and evenly serrated edge upon blades intended for delicate cutting operations. It has been the special object of my invention to provide means whereby .each minute area of the surface to be stropped traverses a constantly shifting path of periodically and continually changing direction on the stropping surface, so as eifectively to prevent tracking. It has also been an object of my invention to so construct my device that during each stroke the pressure varies from maximum to minimum.

The form of my device herein described is but one of many forms which may be designed to perform, in the manner above described, upon the edge to be sharpened, and it is to be understood that my present invention embraces any and all devices providing such relative motion .of blade and abrading means, as hereinafter described, whether such relative motion results from rotation of the abrading means and reciprocation of the blade supporting member as in the present device, or from a combined rotation and reciprocation of the abrading member with or without movement of the blade supporting member as in the device described in my co-pending application Serial No. 404,713, filed November 4, 1929. The peculiar and novel cross-wiping abrading action hereinafter described is the fundamental and essential feature of my invention, hence the appended claims are to be construed as covering any and all devices capable of producing this action.

While my device may by obvious expedients of adaptation be applied to a wide variety of uses, I have shown it as applied toa well-known type of safety razor stropper for re-sharpening doubleedge blades, such as the Gillette blade.

My device may be best understood by reference to the accompanying drawing in which Fig. 1 is a plan view of the stropping elements and the shafts whereon they are mounted and gears connected therewith, the casing and blade support shaft being removed.

Fig. 2 is a longitudinal medial sectional View of my complete device.

Fig. 3 is an end elevation with the case cut away on line 33 of Fig. 2.

Fig. 4 is a diagram showing the path which a point on the blade traverses during one revolution of the gear driven crank.

Referring now more specifically to the drawing, I is a thin pressed metal casing provided with an observation port 2. A pair of parallel hollow shafts 3 and 4 are rotatably mounted within the casing I by means of annular lugs 5 which are formed inwardly from the end walls of the casing I so as to enter the ends of the hollow shafts 3 and 4.

Mounted on shafts 3 and 4, respectively, are strop members 6 and 'I which are provided with end plates 8 which embrace and are rigidly secured to shafts 3 and i. The strop members 6 and I are surfaced with leather or other suitable material. The surfaces of the strop members 6 and I are cylindrical in form, but the axis of each cylinder is slightly displaced from the axis of the shaft whereon it is mounted.

This eccentric mounting of the stropping surfaces is clearly shown in Fig. 3, by the progressively increasing amount of the teeth of the gears 9 and II] which project beyond the surfaces of strop members 6 and I respectively, from the leading toward the trailing edges of the abrading surfaces. In Fig. 3, the position of the axis of rotation of each strop member is indicated by the intersection of the horizontal and vertical solid lines, while the position of the axis of each cylindrical stropping surface is indicated by the intersection of the vertical solid lines with the horizontal broken lines.

The shafts 3 and 4 carry fast thereon gears 9 and I0, respectively, which intermesh. The shaft 3 also carries fast thereon the helical gear II which meshes with a helical gear I2, which is fast on a bushing I3 which rotates on the reduced upper end M of a stud I5, the reduced lower end 16 of which is press-fitted into a hole in the block I! which is secured to the bottom of case I by screws I8. Gear l2 has a different number of teeth from the number of teeth on gear I I.

A rotatable shaft I9 is supported within the casing I at one end, by means of an annular inwardly projecting boss 21! which fits freely over the reduced end 2| of the shaft l9. Slidably mounted on the shaft I9 is the sleeve 22 which is cylindrical in form with a flattened base portion 23, which rests upon the top of bushing I3. Within this flattened base portion 23 is a transverse slot 24 into which projects a crank pin 25 fast in the bushing I3. The upper end of the crank pin 25 carries a hardened roller 26 which contacts with the sides of the slot 24.

A considerable portion 21 of the shaft I9 is formed by cutting away that part of the shaft which lies below a horizontal plane through the axis of the shaft, there being a groove 28 in the diametral surface.

The sleeve 22 is provided With an annular groove 29 and an enlarged bore 30 within which may rotate the collar 3| which carries a key 32 which enters through a keyway 33 and may rotate within the annular groove 29. The collar 3| is slidable upon the portion 21 of shaft l9. Fast mounted within the collar 3! is a bladesupporting member 34 which is semi-circular in cross section, the flat portion being adjacent to the grooved side of the portion 21 of the shaft I9. The flat side of the blade-supporting member 34 is provided with a pair of bosses 35 suitably spaced and shaped to enter the holes in the blade 36 (Fig. 3) to be sharpened. A finger grip 31 is provided at the end of the blade-supporting member 34. The portion 21 of the shaft 19 when supplemented by the blade-supporting member 34 forms a composite shaft, the outer end of which is journaled within a suitable hole in the end of the case i through which these parts project.

The shaft l9 carries fast thereon one member 38 of a Geneva movement, the other member 39 of which is fast mounted on the shaft 3. The shaft 3 is provided with a, crank 40 having ahandle 4|.

The operation of my device is as follows: To insert a razor blade in my device, the crank 40 is turned until the key 32 on the collar 3| is opposite the keyway 33 in which position a slight pull on the finger grip 37 will cause the bladesupporting member 34 to be withdrawn to a position outside the case I so as to expose the lugs 35 and permit the blade 33 to be mounted thereon. The blade-supporting member 34 may then be pushed back into its former position, the blade 36 passing through a suitable slot in the end of case I. The blade is now in position to be operated upon by the revolving strop members 5 and I. As the crank 40 is turned clockwise, the Geneva movement brings the blade 36 to a horizontal position and the leading edges of the strop members 6 and l engage the opposite lower beveled faces of the blade and flex it. The eccentric mounting of the strop members is such as to produce the maximum flexure of the blade and, therefore, the maximum stropping pressure thereon at the outset. As the strop members continue to rotate the stropping pressure decreases to a minimum at the trailing edges of the strop members. This latter condition is shown in Fig. 3. As soon as the strop members pass out of contact with the blade, the Geneva movement operates to rotate the shaft l9 through so as to present the other side of the blade to the strop members. The operation thus far described, excepting the eccentric mounting of the strop members, is that of a present wellknown stropping device.

The rotation of the shaft 3 causes gear II to rotate gear l2 and carry the crank pin 25 in a circular path, thereby reciprocating the sleeve 22 and the connected blade-supporting member 34. This causes a longitudinal wiping action of the blade upon the strop members. If the gears H and I2 were identical, it is obvious that the cycle of this longitudinal wiping action would have the same period as the cycle of the strop members, thus causing a point on the blade to track upon the strop members. To prevent this and produce a varied path upon the siu'face of the strop members of any given point on the blade, I have provided that slight dissimilarity of number of teeth on gears I! and I2 which I have above noted.

It will be apparent from the foregoing that each minute area, or given point on the beveled surface adjacent the edge of the blade traverses a constantly shifting path on the strop members of periodically and continually changing direc tion, i. e., a uniform .angular velocity of the strop members and a varying linear velocity of the blade in a transverse direction, produced by the crank pin mechanism,results in a path upon the strop members for each given point on the beveled surface adjacent the edge of the blade corresponding to a sine curve. This is specifically represented diagrammatically in Fig. 4 in which the distance between the long parallel lines a-a' and b-b represents the stroke of the crank pin 2-5, and, therefore, the maximum width on the strop surface over which any given point on the beveled surface adjacent the edge of a blade will travel. If the mechanism is operated until the strop-ping action begins when the blade is at the extreme outward end of its stroke, I may represent this condition at the point C. As the stropping action continues, the point on the blade corresponding to the point C will trace out the sine curve d on the surface of a strop member. By the time the blade has returned to its extreme outward position, one cycle of this sine 1 curve will have been completed and the point C will have passed to the point e. Due to the fact that the gears H and I2 have a different number of teeth, the strop member will have made a complete revolution at a position corresponding to the point 1; in other words, the cycle of the crank pin is slightly slower than the cycle of the strop members. It is to be noted that the smaller the distance fe (Fig. 4) with respect to distance of, the greater will be the number of revolutions of a'strop member before the point under consideration will traverse the same path again, and if I designate the number of revolutions of a strop member by N, the point will generate N 1 complete sine waves, like that shown, upon the surface of a strop member before retracing the original sine wave d provided the gears II and I2 are designed to secure the best results. Hence, it will be plain from the foregoing that the path upon the strop members of a given point on the beveled surface adjacent the edge of the blade will be a series of sine curves, each slightly displaced from the other and all lying between the parallel lines a-a' and b--b. The angle of the path of travel of a given point on a strop 1 member with respect to the edge of the blade at any position is represented by a tangent to the sine curve for that position. The maximum slope of the sine curve occurs at the points g and h where the tangents are respectively g'g' and h'h'. The line k-k which parallels the line h--ih passes through the point 9 and forms with the tangent gg an angle X within which is included all possible directions of the path of travel of any given point on the strop members with respect to the edge of the blade. It will be observed from Fig. 4, that the angle X can be increased either by increasing the spacing between the lines aa' and bb' thereby increasing the ordinates of the sine curve which means I have secured the often appear on the face after shaving.

best results with my device when it is organized to produce the curve (1 (Fig. 4) which is drawn to scale and represents a'stroke of the reciprocating sleeve of and distance cf=l6 ,fe which is easily interpreted as representing 16 revolue tions of the strop members and N1 or 15 revolutions of the crank gear l2 before tracking occurs. This arrangement with 16 revolutions of the strop members to a complete stropping cycle, makes the angle X just slightly less than A microscopic examination of commercial razor blades discloses irregularities in the edges which project beyond the peak of the average serration and which appear to be particles partially torn away from the edge portion of the blade by a local coarseness in the grinding abrasive. These irregularities are directly responsible for the minute nicks and blood spots which Although the blade may be very sharp and may cut freely without pulling, the skin-nicking effect may be present. If, in the stropping operation, such irregularities track upon the stropping surface it will be ineffective to remove them. My device, because of the non-tracking feature above described, and the periodic change in the angle of wiping is very effective in removing these irregularities and in producing a finely and evenly serrated edge.

Because of the continued gradual reduction of pressure during each stroke of the stropping action resulting from the eccentric mounting of the strop members, the stropping compound which has initially been distributed uniformly over the strop surface will gradually be worked toward the trailing edge of the stropper, the deposit becoming thickest there so as to give the finest polishing effect during the latter portion of each stroke, the final stroke concluding With this action.

While I have illustrated and described the proportions and ratios which give the best stropping action it is to be understood that variations may be made in the gear ratios and stroke without serious loss in effectiveness and therefore my claims are written to cover any and all devices of the character specified wherein the variation in maximum stropping angle exceeds 20 degrees and is associated with a non-tracking feature involving an harmonic curve having Waves displaced one from the other upon the surface of a strop member.

Having thus fully described my invention, what I claim is:

1. In a device of the character specified, the combination of a blade supporting member, a strop member, rotative means and reciprocating means whereon said members are mounted, and means operatively connecting said rotative means and said reciprocating meansand adapted to impart thereto periodic motions having a small frequency differential, thereby generating such relative motion between said members that each minute area on the beveled surface of a blade mounted on said blade supporting member may traverse on the surface of said strop member a constantly shifting sinusoidal path, the successive Waves of which are slightly displaced due to said small frequency diiferential.

2. In a device of the character specified, th combination of a slidably and removably mounted blade supporting member, a rotatable strop member, a reciprocating member to which said blade supporting member is detachably and operatively connectedQa crank means adapted and.

arrangedtooperate said reciprocating member, a gear whereon-said crank means is mounted, and a second gear mounted on said rotatable strop member and adapted and arranged to mesh with and drive said gear whereon said crank means is mounted, said gears differing by one in number of teeth'to provide cross-wiping and non-tracking abrading action substantially as specified. I

3. In a device of the character specified, the combination of a slidably mounted blade supporting member, a rotatable strop member, crank means for actuating said blade supporting member, a gear whereon said crank means is mounted,

and a second gear mounted upon said rotatable strop member, and arranged to engage with and drive said first mentioned gear,,said gears being adapted and arranged as specified to impart such relative motion to said members that each elemental area on a beveled surface adjacent the edge of a blade mounted on said blade supporting member may move over the surface of said strop member generating thereon an harmonic curve of wave length approximating but not equal in magnitude to the circumference of said strop member.

4. In a device of the character specified. the

combination of a blade supporting member, a' rotatable strop memberhaving a cylindricalsurface mounted eccentrically with respect to the axis of rotation, and means combining rotative and reciprocating movements differing in frequency; one from the other, for so imparting relative motion to said members that an elemental area on a beveled surface adjacent the edge of a blade mounted on said blade supporting member may move over the eccentric cylindrical surface of said strop member and generate thereon an harmonic curve having the successive waves slightly and equally displaced one from the other, the pressure between said blade and said cylindrical surface varying progressively and periodically from maximum to minimum with each revolution of said strop member.

5. In a device of the character specified, the combination of a slidably mounted blade supporting member, a rotatable strop member, crank means for actuating one of said members, and a pair of gears operatively connecting said crank means with the other of said members, said gears being adapted and arranged substantially as specified to so impart relative motion to said members that the beveled surface adjacent the edge of a blade mounted on said blade supporting member may be progressively polished as a. result of each elemental area thereon being rubbed against a progression of elemental areas on the surface of said strop member lying along an harmonic curve the successive waves of which are slightly displaced one from the other and have a maximum slope angle of at least 10 degrees.

6. In a device of the character specified, the combination of a blade supporting member, a rotatable strop member having a cylindrical surface the axis of which is displaced from the axis of rotation, and means combining rotative and. reciprocating movements differing in frequency, one from the other, arranged to so impart relative motion to said members that the beveled surface adjacent the edge of a blade mounted on. said blade supporting member may be progressively polished as a result of each elemental "4 V enema? face the. axis of which is displaced from the axis of rotation, and; means combining rotative and reciprocating movements differing in frequency, one from the other, arranged to so impart relative motion to said members that abrading compound applied to said strop member will be automatically distributed uniformly along any line on the surface of said strop member and parallel to the axis thereof, and progressively deeper from the leading to the trailing edge of said 10 strop member.

AR'IH-UR- J. HOLMAN. 

